Thermoplastic synthetic resins have, among their attributes, a property when they come into contact with gases or liquids, especially aliphatic or aromatic hydrocarbons, that the gas or liquid can diffuse in or through the thermoplastic synthetic resin.
This property, referred to as permeation or penetration of the thermoplastic synthetic resin by the fluid medium can be pronounced and can affect thermoplastic synthetic resins used as containers for these fluids, used as enclosures from which these fluids are to be excluded, or used as conduits through which these fluids are to flow or through which fluids are to flow which are to be protected from the diffusing fluids.
The diffusion of gases or liquids through containers or conduit walls is, as a rule, highly undesirable, especially when the diffusing medium is toxic or noxious or may constitute a contaminant.
In order to minimize the leakage which can result from such diffusion, it is customary to make the walls formed from the thermoplastic synthetic resin sufficiently thick to minimize or exclude such diffusion. That, of course, is highly expensive. The diffusion coefficient, of course, is a measure of the rate at which the diffusing molecules, i.e. the molecules of the fluid medium, migrate through the wall in the direction of the concentration gradient. The diffusion coefficient is as a rule measured in m.sup.2 /s.
In order to minimize diffusion as described, it has already been proposed (see German patent 41 02 181) to incorporate an additive in the thermoplastic which will reduce the diffusion of hydrocarbons through the thermoplastic material. The additive itself is a thermoplastic and can comprise a thermoplastic carrier, polyvinylidenefluoride and aluminum stearate. The aluminum stearate serves as a binder between the polyvinylidene fluoride and the thermoplastic carrier material. When hydrocarbons penetrate the thermoplastic synthetic resin blended with this additive or reacted therewith, the presence of the aluminum stearate results in a liquid thickening or gelatinization of the hydrocarbons which significantly reduces the hydrocarbon diffusion.
The synthetic resin reacted with this additive, however, still has a relatively high diffusion coefficient and, over long stand times or periods of use of this thermoplastic synthetic resin as a hydrocarbon container, relatively high loss rates of the fluid medium stored in the container can be observed. This is highly problematical especially when toxic and noxious media are concerned. The synthetic resin containing the additive has been found to be only slightly resistant to UV light so that after prolonged exposure to sunlight, there can be some decomposition and structural change in the container. Furthermore, the antistatic properties of the thermoplastic synthetic resin provided with this additive leave much to be desired.